Presently it is proposed to build large structures in space by partially assembling by welding, bolting, etc., large structural components together and then transporting the partially assembled components into space where the components are to be assembled to complete the space structure. Such approach requires many launchesa, including space trips to insert the components into orbit and space trips to insert the men and tools into orbit with the components to complete the assembly. The device of the present invention utilizes the properties of space for the construction of large structures, including environmental habitats and/or protective shells, etc., without regarding excessive launches and without requiring men to be in orbit for long periods of time to complete the construction. For structures such as habitats, the use of man-hours in space suits are minimized. The internal construction is done in an enclosed space which is inflated by breathable gases to provide an Earth-like environment, with no requirement for space suits.